code: def next_variables(self, tx):
      unimplemented("abstract method, must implement")
  
imports: import itertools
  import operator
  from typing import Dict, List, Optional
  from ..None import polyfill, variables
  from ..exc import unimplemented
  from .base import MutableLocal, VariableTracker
  from .constant import ConstantVariable
label_desc: Use image node_id 2 for calling the IteratorVariable obj's underlying member method code with example usage: obj.next_variables(tx) without return types